Known in the art are interferometers for checking the shape of convex spherical surfaces of lenses based on the employment of test glasses and compensators (zero-correctors) (cf. Saunders I. B., I. Res. Nat. Bur. Stand., 1954,53, No. 1, p. 29). Test glasses do not make it possible to check the surface in a single pass since the diameter of the test glass is substantially smaller than the diameter of the surface being checked, and a repeated aplication of the test glass to the checked surface takes much time. In addition, the contact of the test glass with the checked surface requires a careful preparation of the surface for the checking procedure. In case the surface radius is changed in view of the manufacturing considerations, a new test glass should be made which raises the cost of the check procedure.
Known in the art are interferometers using compensators which transform a planar or spherical wavefront into a wavefront of a desired configuration. (cf. G. V. Kreopalova, D. T. Puryaev, Studies and Check-up of Optical Systems, M., Mashinostroenie Publ., 1978).
In such interferometers the problem of checking resides in obtaining information on errors of the surface being checked simultaneously in all zones thereof, rather than in individual areas. This problem is solved by using a compenstor which is so designed as to direct light rays in the form of a homocentric beam having its vertex coinciding with the center of the convex spherical surface being checked. In case the latter is on the lens, the compensator should be designed to take into account the action of the other surface of the lens so as to check the convex surface in the same manner as a concave surface which is checked from the center of curvature. This operation requires the use of a plurality of individual compensators since each compensator can only be used for checking a lens of a predetermined configuration.
In applications where the surface being checked is the surface of an optical component made of an opaque material, the interferometer based on the use of a compensator cannot be used at all for checking convex surfaces by means of beams directed into the interior of the material of an optical component.
Known in the art is an inteferometer designed for checking the shape of convex spherical surfaces of optical components, comprising a monochromatic light source and a sequence of devices therebehind in the path of beams including a focusing lens, a light splitter, a compensator, a lens system having its downstream surface which comprises a reference concave spherical surface having a center of curvature which is optically matched with the back focus of the focusing lens and a system for recording the interference pattern (cf. Yu. V. Kolomiytsov, Interferometers, L., Mashinostroenie Publ., 1976, p. 204-211.)
This interferometer makes it possible to check spherical surfaces of optical components of comparatively small diameters (smaller than 100-150 mm) and with a certain ratio D/R, wherein D is the diameter and R is the radius of the surface being checked.
The employment of the prior art interferometer is hampered in checking convex spherical surfaces of greater diameters (of the order of 500-600 mm) and with other ratios of D/R since it requires the replacement of the lens system with the reference surface and lens consuming adjustment operations, and the size of the interferometer of the prior art type is unnecessarily large.